This invention relates to mooring and cargo handling systems of the type which transfer cargo through conduits that extend from a shore or other primary installation to a ship while the ship is free to drift about its mooring point.
A variety of liquid cargos can be transferred to or from large tankers by mooring and cargo handling systems that lie in the sea and which are connected by pipelines that run along the sea bottom to the shore or to a nearby floating installation. Such systems include an anchored buoy to which the ship can be moored, and one or more hoses that can extend to the ship. The system is normally constructed so that a ship which is moored to the buoy and connected to the cargo-transfer hoses, can drift freely about the buoy. This is accomplished by utilizing a cargo swivel unit with a lower section connected to the undersea conduits and an upper section rotatably mounted on the lower section and connected to hoses that lead to the ship.
The design of mooring and cargo transfer systems is complicated in the case of certain types of cargos. Liquified natural gas (LNG) is one type of cargo which is difficult to handle because it can evaporate during the transfer, and because the evaporated LNG can become dangerous if large quantities leak into the environment. Such leakage can occur at the swivel unit through the rotary seals thereof. Another type of cargo which is difficult to handle is a slurry containing hard or abrasive particles that can hamper proper operation of the bearings of the swivel unit if allowed to leak into the bearings. A cargo transfer system which facilitated the transfer of difficult cargos of these types would have wide application in the ship transport of materials.